1. Field of the Invention
The present invention relates to fuel vapor processing apparatus for processing fuel vapor that may be produced within a fuel tank.
2. Description of the Related Art
Known fuel vapor processing apparatus generally include a fuel tank, a canister for adsorbing fuel vapor that may be produced in the fuel tank, and an aspirator that produces a negative pressure by a part of fuel discharged from a fuel pump disposed within the fuel tank. Therefore, fuel adsorbed by the canister can be recovered into the fuel tank by utilizing the negative pressure produced by the aspirator. Such a fuel vapor processing apparatus is disclosed, for example, in Japanese Laid-Open Patent Publication No. 2002-235608. In the fuel vapor processing apparatus disclosed in this publication, a jet pump serving as an aspirator indirectly communicates with the fuel pump via a pressure regulator. As the fuel pump is driven during running of an automobile, surplus fuel discharged from the fuel pump is released into the fuel tank via the pressure regulator. The surplus fuel released from the pressure regulator is introduced into the aspirator for producing a negative pressure. The aspirator is disposed in the midway of a recovery passage. A front opening of the recovery passage, i.e., a discharge opening for discharging the fuel recovered from the canister and the surplus fuel introduced into the aspirator is submerged within the fuel stored within the fuel tank.
This kind of fuel vapor processing apparatus is used for preventing potential damage to the fuel tank due to increase of the internal pressure that may be caused by the production of the fuel vapor. However, in the case of the arrangement of the above publication, the aspirator normally operates continuously as long as the fuel pump is driven to release the surplus fuel. Therefore, even after the fuel vapor adsorbed by the canister has been completely recovered, the aspirator still continuously operates. In addition, because the adsorbed fuel and the surplus fuel recovered by the aspirator are discharged into the fuel stored within the fuel tank, unpleasant and unnecessary bubbling may occur in the fuel of the fuel tank even after completion of recovery of the fuel. This may enhance the production of fuel vapor within the fuel tank and the internal pressure within the fuel tank may be unnecessarily increased.
Further, in the case of the arrangement of the above publication, the aspirator communicates with the fuel pump via the pressure regulator. This means that the surplus fuel is introduced into the aspirator from the pressure regulator. Therefore, the flow rate of the fuel introduced into the aspirator may become unstable, leading to unstable ability for recovering the fuel. Therefore, it may be considered to make direct communication between the aspirator and the fuel pump such that a part of the fuel for feeding to the engine under pressure by the fuel pump is directly introduced into the aspirator. However, because the aspirator continuously operates even after completion of recovery of the fuel, an amount of the fuel that is more than necessary may be introduced into the aspirator to adversely affect to the stability in supplying the fuel to the engine. For example, a maximum amount of the fuel capable of being supplied to the engine may be reduced by the amount of fuel introduced into the aspirator. Therefore, it may be possible to cause shortage of supply of the fuel to the engine when the engine operating condition requires a large amount of fuel.
Further, the fuel vapor processing apparatus of the above publication includes a heater that heats inside of the canister for effectively desorbing the fuel from the canister during recovery of the fuel. Although not explicitly disclosed in this publication, an engine control unit (ECU) is generally used for controlling the operation of a process system of this kind of fuel vapor processing apparatus.
In the case of the fuel vapor processing apparatus of the above publication, the process system is operated for processing the fuel vapor as long as the engine operates. Thus, the process system is operated regardless of the amount of the fuel vapor adsorbed within the canister (i.e., the amount of the fuel remaining within the canister). Therefore, even after the fuel within the canister has been actually substantially completely desorbed, the process system still continues to operate. This leads to unnecessary consumption of an electric power needed for operating the heater, resulting in unnecessary consumption of the fuel. In order to avoid this problem, it may be possible to control the fuel pump to process the fuel vapor independently of the operation of the engine. However, also in this case, it may be possible that the fuel pump continues to be driven even after completion of recovery of the fuel. Therefore, this may lead to unnecessary consumption of electric power needed for operating the fuel pump in addition to the heater.
The value of the negative pressure produced by the aspirator may depend on the amount of the fuel introduced into the aspirator. Thus, the value of the negative pressure increases as the amount of the fuel introduced into the aspirator increases. On the other hand, the value of the negative pressure decreases as the amount of the fuel introduced into the aspirator decreases. In the case of the arrangement of the above publication, the surplus fuel discharged from the pressure regulator is introduced into the aspirator. In other words, the fuel pump indirectly communicates with the aspirator via the pressure regulator. For this reason, the amount of fuel introduced into the aspirator tends to be unstable, leading to unstable negative pressure. Therefore, the remaining amount of the fuel within the canister for an accumulated operation time of the process system tends to be unstable. Hence, it is difficult to determine the remaining amount of the fuel within the canister and it is also difficult to appropriately determine when the process system is to be stopped
Therefore, there is a need in the art for a further improved fuel vapor processing apparatus.